Separation of the constituents of gaseous mixtures



March 11,1947. Q C', VAN Nuys 2,417,279

SEBARATIONOF THE CONSTITUENTS 0F GASEOUS `MIX'IURES Filed July 22, 1944 lill Inl'

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Patented Mar. l1, 1947 UNITED STATES PATENT OFFICE 2,417,279 SEPARATION OF THE CONSTITUENTS OF GASEOUS lVIlXTURES Claude C. Van Nuys, Greenwich, Conn., assignor to Air Reduction Company, York, N. Y., a corporation of Incorporated, New New York Application July 22, 1944, Serial No. 546,153 8 Claims.V (Cl. (i2- 1755) plish the desired purpose, but are subject to cer-- tain disadvantages, including incidental losses and particularly the cost of the energy employed in compressing the gaseous mixture.

Itis the object of the present invention to provide a highly enicient method involving minimum expense whereby the constituents of a gaseous mixture such as air may be recovered in a commercially practicable manner.

Another object of the invention is the provision of a method whereby the three constituents of the mixture are separated and recovered in substantial purity.

A further obj ect of the invention is the economical utilization of an external cooling system t eil'ect the necessary liquefaction ofthe ternary gaseous mixture prior to separation of the constituents thereof.

other objects and advantages of the invention will be apparent'as it is better understood by'reference to the following specification and the accompanying drawing, which illustrates diagrammatically an apparatus adapted for use in practising the invention.

In the drawing, no attempt has been made to illustrate those details of liquefaction apparatus which are well known in the art, the purpose of the drawing being merely to assist the .reader to a complete comprehension of the essential features of the invention. Devices well known inl the art may be utilized, and the form and arrangement of the apparatus will conform in general to the means commonly employed to accomplish similar functions.

In order to clarify the description, reference will be made to a ternary mixture such as air, consisting of nitrogen, oxygenand argon. The constituents neon, such relatively small amounts that no considera- ;ion need be given thereto in respect to the sepiration hereinafter described. Ternary mixtures iaving constituents the physical characteristics f which are related as in the case of nitrogen,

krypton and xenon occur'in oxygen andargon, may be treated similarly to effect the desired separation.

It is an important advantage of the present invention that the three constituents are each recovered in substantial purity and that all of such constituents present in the gaseous mixture treated are recovered. A further advantage arises from the fact that the gaseous mixture treated, for example air, is not utilized to any extent to maintain the refrigeration necessary to the successful operation of the procedure. A separate refrigeration cycle is utilized. Hence the gaseous mixture, for example air, entering the system need be compressed only to relatively low pressure, for example a pressure not exceeding 5 atmospheres absolute. Many of the losses incidental to procedures as previously known have been due to the utilization of the gaseous mixture undergoing separation as the refrigerating medlum.

In the application of the invention to the separation of the constituents of air, three products are obtained; namely, (1) substantially pure nitrogen with only minute percentages of oxygen and practically no argon; (2) oxygen of industrial purity containing less than 0.5% of impurities of any sort; and (3) practically all of the argon originally present in the air with only small percentages of oxygen and no nitrogen.

To attain this result, the separation is eiected in a relatively simple manner. After initial compression to a relatively low pressure, the air'is cooled in exchangers by heat interchange with products of the separation. Thereafter it is sep arated into two liquid fractions by heat provided as hereinafter described. The separation affords a -fraction` enriched in oxygen, usually containing approximately 4,0% 'ofoxygem and a liquid consisting `of nitrogen.l The ,tw'o liq'- uidsare then rectified to afford an elii'uent consisting of pure nitrogen and a vapor taining all of the oxygen, all of the argon, and a small proportion of nitrogen.' At thisl point 'the nitrogen eiiiuent is withdrawn as one of 'the' products to be supplementedwith nitrogen recovered from the vapor. phase consistingjprincipallylolf oxygen and argon.

The vapor phase is withdrawn and subjectedl initially to selective liquefaction by vheat exchange` By this means most v0i' separated from a liquid exchangey with liquid nitrogen and they vapor therefromk phase confthen subjected to an auxiliary rectification.

drawn and added to the eiiluent from the initial rectification.

The liquid consisting of oxygen and argogh is e vapor at the top of the rectification consists of argon which may still include a slight percentage of nitrogen as an impurity. Itis, therefore, subjected to selective condensation by heat exchange with liquid nitrogen which aords a reflux liquid consisting of pure argon. The residual nitrogen which is thus separated is delivered to the effluent from the primary rectication.- The provision of the reflux liquid consisting of pure argon assures a pure argon vapor which may be withdrawn as one of the products from the auxiliary rectification. The liquid accumulating at the bottom of the auxiliary rectification is pure oxygen. It may be withdrawn as a` liquid or vaporized and delivered as a vapor from the rectiflcation.

As will be readily apparent from the foregoing description, the three constituents are recovered in substantial purity. Moreover, none of the `constituents is lost, since there is no impure waste gas or mixture of gases which must be discharged from the system. The procedure insures an efficient and economical separation and recovery of the several constituents of the mixture.`

As already indicated, the method does not rely upon compression of the gaseous mixture kto be separated to aord the 'necessary refrigeration. The liquid nitrogen which is utilized to maintain the requisite low temperatures at the places required in the system is provided by. compression of nitrogen which is circulated in an independent cycle. After compression and cooling,.the nitrogen is liqueed. The liquid nitrogen isdelivered to the several condensers where it performs its function in cooling the gaseous mixture and the constituents thereof. The liquid nitrogen is vaporized, and the vapor, after giving up its cold, is recompressedand again utilized for refrigeration of the system. Although it is not essential, a. portion of the nitrogen may be expanded from its initial pressure in a suitable expansion engine or turbine to afford the additional refrigerative effect, depending upon expansion of the gas with external work.

An important advantage of the present pro-A cedure arises from the fact 'that eiiluent nitrogen from the primary rectification, is mingled with the nitrogenof the independent cycle and only a sufficient amount of the cold nitrogen is delivered through the exchanger for heaty exchange with the incoming gaseous mixture. 'Ihis avoids premature condensation of the entering gaseous mixture and also amply makes up for any loss of nitrogen inv the independent cycle in which the nitrogen is liquefied to afford refrigeration at various points in the system.

- The details of the invention will be better unsoL derstood by reference to the following description and the drawing, in which 5 indicates a rectification column having trays 6 and the usual bubble caps 1. The column is closed at its top by a diaphragm 8, and an outlet 9 is connected thereto to deliver the eiiiuentnitrogen which is separated in the rectification of air.

The air is introduced, after initial compression and cooling, through a pipe I9 to an exchanger II and circulated about tubes l2 and I3 therein, being cooled by nitrogen delivered to the exchanger as hereinafter described. The air passes through a pipe I4A to a condenser I5 above the column 5 and passes through tubes I6 thereof 4 in heat exchange relation with liquid nitrogen and vapors thereof supplied through a pipe I1. The liquid nitrogen flows over baiiles I8 and is vaporized while the air flowing through the tubes I6 is subjected to selective liquecation. As a result, liquid rich in oxygen is delivered to a collector I9 and thence through a pipe 2|! and pressure reducing valve 2I` to an intermediate level of the column 5.

The residue from the condenser I5 is delivered through a pipe 22 to the tubes 23 of a condenser 24 which is supplied with liquid nitrogen by a. pipe 25. The residual nitrogen in the tubes 23 is liquefied and collected in a collector 2B. It is delivered through a pipe 21 and pressure reducing valve 28 to the top of column 5, thus affording reflux nitrogen for the primary rectification. The surplus liquid nitrogen and vapors therefrom escape from the condenser 24 through an overflow 29 and thence to the pipe I1, which delivers the liquid and vapors to the condenser I5. The nitrogen vapor from the condenser I5 is withdrawn through a pipe 30, to which the pipe 9 is connected, so that the eiiiuent from the primary rectification is mingled with the nitrogen'vapor from the condensery I5. The vapor is cold and is utilized as hereinafter described as a cooling medium for nitrogen undergoing liquefaction in the independent nitrogen cycle.

The nquia accumulating in the bottom ofthev column 5, consisting principally of oxygen and argon, is vaporized by gaseous nitrogen circulating through a coil 3| as hereinafter described, to afford vapor in the column and alsovapor which is withdrawn through a pipe 32. The vapor thus withdrawn includes all of the oxygen` and argon initially present in the air treated. It is delivered to a condenser 33 and passes upwardly through tubes 34 thereof, being subjected to heat exchange with liquid nitrogen supplied through a pipe 35 and throttle valve 36. Inthus passing through the tube-s 34,v the gaseous mixture .is liquefied except for residual nitrogen which escapes thro-ugh a pipe 31 controlled by avalvek 38. The pipe 31 is connected tothe pipe 30 so that the residual nitrogen joins the eflluent from the primary rectification and the `nitrogen vapor from the condenser I5. The lliquid consisting of oxygen and argon with possibly some relatively small proportion of nitrogen is delivered through a pipe 39 and valve 40 to an auxiliary rectier 4I which is provided with the usualtrays 42 and bubble caps 43.

As the liquid flows downwardly through the' column, it is gradually enriched in oxygen,'where as the vapors rising through the column are enriched in argon and carry also any small proportion of nitrogen which may be present. The

vapors pass upwardly through tubes 44 of a con-- to the tubes 5I of an exchanger 52 where it serves.

to cool nitrogen in the independent cycle as hereinafter` described. The argon is withdrawn through a pipe 53 and delivered to suitable storage receptacles. It affords one oi the products of the operation.

'I'he liquid accumulating in the bottom of the column 4I is vaporized by nitrogen passing through a, coil 54, supplied as hereinafter described, to afford the vapor necessary in the column, and if desired to permit withdrawal of oxygenv vapor through a pipe 55 and valve 56. Liquid oxygen may, however, be withdrawn through a.

pipe 51 and delivered by a pump 58 to a pipe 59 which carries the oxygen to the tubes I3 of the exchanger II.` The oxygen is withdrawn from the exchanger through a pipe 60 and delivered to suitable storage receptacles aifording the second product of the operation.

To provide necessary refrigeration, nitrogen is compressed in a compressor 6| and is delivered by a. pipe 62 to a cooler 63 and thence by a pipe 64 to the exchanger 52 in which it circulates about tubes 5I and 65 in heat exchange with argon and cold nitrogen returning in the cycle. The nitrogen is delivered from the exchanger through a pipe 6E and a, portion thereof may, if desired, be diverted through a pipe 61 to an expansion engine 68 where the nitrogen is expanded with external work and further cooled. The expanded nitrogen passes through a pipe 69 to a liqueer 10 and circulates about tubes 1I therein.

'I'he balance of the nitrogen is delivered through a pipe 'I2 to the coil 3| in the bottom ofthe column 5. After passing through the coil, the nitrogen returns through a pipe 13. A portion of the nitrogen froml the pipe I2 may be diverted through a pipe 14 to the .coil 54 in the bottom of the auxiliary column 4I. Some of the nitrogen may be liquefied in passing through the coils 3| and 54. After passing through the coil, the nitrogen returns through a pipe 'I5.

Nitrogen from the pipes 13 and I5 is combined in the pipe 16 and delivered to the top of the liqueer 10. Passing downwardly through the tubes 1I, liquefaction of the nitrogen is completed and the liquid is withdrawn through a pipe 'l1 which is connected to the pipe 25 delivering liquid nitrogen to the condenser 24 and also to the pipes 35 and 46 which deliver liquid nitrogen to the condensers 33 and 45. The liquid nitrogen vaporized in condensers 33 and 45 are conducted by pipes 96 and 35 and combined in the pipe 31' which delivers these vapors to .the pipe 30.

The gaseous nitrogen in the pipe 30 is also delivered to the liqueer 'IIJ circulating about the tubes 1I therein, thus affording additional cooling medium to effect liquefaction of nitrogen in the tubes 1I. A portion of the nitrogen flowing through the liqueer I0 about the tubes 'II thereof is withdrawn through a pipe 'I8 and delivered to the exchanger 52. After flowing through the tubes 65 thereof, it is returned by a` pipe I9 to the compressor 6| and thus re-circulated in the independent nitrogen cycle. The balance of the nitrogen, after circulating about the tubes 'II of the liquefier 10, is Withdrawn through a pipe 80 which delivers it to the exchanger II. After circulating through the tubes I2 thereof, the nitrogen is withdrawn through a pipe 8| and delivered to suitable storage receptacles. This nitrogen" affordsthe third product of kthe separation.

The nitrogen may be compressed in the compressor 6I to any suitable pressure adapted to afford the necessary refrigeration to maintain the cycle. This necessary refrigeration will de the present invention,

pend upon various leakage losses and other press the nitrogen to pressures as high as those frequently used` in systems where the gaseous mixture under separation is utilized .as the refrigerating medium, that is, 15-20 atmospheres absolute. The use of a separate nitrogen cyclefor refrigeration introduces marked efficiency in the operation of the system because less expenditure of work is necessary to effect the separation.

As previously indicated, the expansion engine 68 and its connectionsmay be omitted. Especially in smaller plants, expansion with external work may not be feasible because of the limitation of practical sizes of expansion engines and turbines adaptedv for the purpose. In larger plants, the use of the expansion engine is desirable since it increases the efficiency of the system.

The method as described ensures maximum recovery of the three desired constituents with minimum losses of such constituents and particularly the avoidance of contamination of the desired constituents with others. Thus, nitrogen-free argon is highly desirable for certain industrial purposes. Pure nitrogen and pure oxygen also have Wide uses, and freedom from impurities is an important requirement in respect to these gases. The procedure permits the production of all three constituents in the desired purity and simultaneously.

It has been indicated that all of the cold nitrogen recovered as the eiiluent or by vaporization of liquid nitrogen is combined. Utilization of therefrigerative effect of this nitrogen in initially liquefying nitrogen in the independent cycle avoids the possibility of affording too much refrigeration in the incoming gaseous mixture with consequent premature liquefaction. Such liquefaction in the case of air affords liquid air, whereas efficiency of separation in accordance with the invention requires the delivery ofthe gaseous /mixture to the tubes I6 of the condenser I5 in the gaseous phase, so that a liquid enriched in oxygen may be secured. In accordance with the gaseousmixture enters the tubes I6 of'the condenser I5 only in the gaseous phase, since premature liquefaction in the exchanger I I is avoided.

Various changes may be made in the details of procedure and in the apparatus employed without departing from the invention or sacrificing the advantages thereof.

Iclaim:

1. The method of separating the constituents of ternary gaseous mixtures which comprises liquefying the gaseous mixture in two fractions by indirect heat exchange with a refrigerating liquid and thereby vaporizing the liquid, rectifying the two fractions to separate an eiliuent consisting of the most volatile constituent, mingling the eiiluent and the vaporized liquid, utilizing the mingled gases to cool and liquefy a recompressed -portion thereof to afford the refrigerating liquid,

gen, withdrawing the remainder ing the two fractions to separate an eiiiuent consisting oi' the most. volatile constituent, mingling the eiiiuent and the vaporized liquid, utilizing the mingled gases to cool and liquefy a recompressed portion thereof to afford the refrigerating liquid, withdrawing the remainder of the mingled gases, withdrawing a vapor from the rectication consisting essentially of the other two constituents ofthe gaseous mixture and separating ythe constituents of that vapor by an auxiliaryrectication.

3. The method of separating nitrogen, oxygen and argon from air which comprises liquefying the air in two fractions by indirect heat exchange with liquid nitrogen, thereby vaporizing the liquid, rectifyingl the two fractions to separate an eilluent consisting of nitrogen, mingling the eiliuent and the vaporized liquid nitrogen, utilizing the mingled gases to cool and liquefy a recompressed portion thereof to afford the liquid nitrogen, utilizing the remainder of the mingled gases to cool the incoming gaseous mixture, withdrawing a vapor from the rectification consisting essentially of oxygen and argonv and separating the oxygen and argon by an auxiliary rectification.

4. The method of separating nitrogen, oxygen and argon from air which comprises liquefying the air in two fractions by indirect heat exchange with liquid nitrogen, thereby vaporizing the liquid, rectifying the two fractions to separate an eiiiuent consisting of nitrogen, mingling the efiiuent and the vaporized liquid nitrogen, utilizing the mingled gases to cool and liquefy a recompressed portion thereof to afford the liquid nitroof the mingled gases as the nitrogen product, withdrawing a vapor from the rectification consisting essentially of oxygenand argon and separating the oxygen and argon by an auxiliary rectification.

5. The method ofY separating the constituents of ternary gaseous mixtures which comprises maintaining a refrigerating cycle by compressing and cooling a gas to provide a refrigeratingliquid,

vaporizing the liquid by heat exchange with the gaseous mixture whereby the latter is liquefied in two fractions, rectifying the liquid fractions to separate gaseous efiluent consisting of the most volatile constituent, adding the eiliuent to the vapor from the'refrigerating liquid, utilizing the efiluent and vapor to cool and liquefy a portion thereof in the refrigerating cycle, utilizing the remainder of the eluent and vapor to cool the incoming gaseous mixture, withdrawing a vapor from the rectification consisting essentially of the other two constituents of the gaseous mixture and separating the constituents ofthat vapor byv an auxiliary rectification.

6. The method of separating the constituents to separate gaseous eiuent consisting of the most volatile constituent, adding the eiiluent to the vapor'from the refrigerating liquid, utilizing the effluent and vapor to cool and liquefy a portion thereof in the refrigerating cycle, withdrawing the remainder of the eluent and the Vapor from."

the refrigerating liquid, withdrawing a vapor from the rectification consisting essentially of the other two constituents of the gaseous mixture and sep- Y arating the constituents of that vapor by an aux.. iliary rectification. l

7. The method of separating nitrogen, oxygen and argon from air which comprises, maintaining a refrigerating cycle by compressing and cooling nitrogen to provide liquid nitrogen, vaporizing the liquid nitrogen by heat exchange with air whereby the latter is liquefied in two fractions, rectifying the liquid fractions to sepa-ratea gaseous eflluent consisting of nitrogen, adding the effluent to vaporized liquid nitrogen, utilizing the resulting nitrogen product to cool and liquefy a portion there-1 of in the refrigerating cycle, withdrawing the remainder of the nitrogen product, withdrawing a vapor from the rectification consisting essentially of oxygenand argon and separating thev oxygen and argon by an auxiliary rectification.

8. The method of separating nitrogen, oxygen and argon from air which comprises, maintaining a refrigerating cycle by compressing and cooling nitrogen to provide liquidA nitrogen, vaporizing theliquid nitrogen by heat exchange with air whereby the latter is liqueed in two fractions, rectifying the liquid fractions to separate a gaseous eiliuent consisting of nitrogen, adding the eilluent to the said vaporized liquid nitrogen,

utilizing the resulting nitrogen product to cool and liquefy aportion thereof in the refrigeratlng cycle, withdrawing the remainder of the nitrogen product, withdrawing a vapor from the rectificailiary rectification. Y

CLAUDE c. VAN NUYs.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTSv Number Name Date v2,240,925 De Baufl May 6, 1941 l Wilkinson Mar. 8, 1927 

